1. Field of the Invention
The invention relates generally to lithographic image development and resulting products.
The invention relates more specifically to a lithographic process used for fabricating a pattern-defining resist layer on a semiconductor or other substrate where the resist layer is to include apertures of submicron dimensions.
2. Description of the Related Art
Economic mass-production of devices with microscopic features of ever decreasing dimensions has been a long-standing goal of the semiconductor and other arts.
In commercial settings, submicron microscopic features are often defined on a semiconductor or other substrate by way of direct contact masking. A masking layer (e.g., a photoresist layer) is deposited directly onto a substrate surface. A pattern of apertures (windows) is defined through the masking layer using photolithographic development means or other pattern-defining means. The masking layer is then hardened to resist radiation, dopants, etchants, metallization materials, and/or other agents which are to be next applied to the substrate.
When the expected radiation, dopants, etchants, metallization materials, and/or other agents are next applied, they pass selectively through the apertures (windows) of the hardened masking layer and thereby selectively contact and/or alter exposed portions of the underlying substrate surface.
A broad range of uses can be found. In the semiconductor production field, a masking layer with a desired pattern of apertures is useful for, but is not limited to: (1) defining a P-type or N-type conductivity region at an exposed portion of the substrate (e.g. by passing doping agents through the apertures), (2) defining an electrically insulative region at an exposed portion of the substrate (e.g. by exposure to an oxidizing agent), (3) selectively etching away substrate material exposed by the masking layer aperture (e.g. by exposure to an etching agent), (4) developing a metallic contact to the exposed substrate area, and (5) developing a metallic interconnect line which couples one exposed substrate area to another.
Defining openings or apertures through the masking layer is a critical step within the overall process. Lithographic patterning processes are commonly used. The patterning processes can be characterized as two basic kinds; laboratory implementations, and commercially practicable, mass-producible techniques.
There are many proposals to use X-ray or other short wavelength radiations, in a direct-write or stepper-duplicated mode, for defining submicron features either on a resist layer or directly on a substrate. But these techniques are still more in the nature of laboratory implementations, rather than commercially viable techniques.
For the time being, the commercially viable techniques can be said to be those which rely on wavelengths longer than approximately 365 nanometers and on stepper optics.
The relatively long wavelength (0.365 microns or larger) of currently available, commercially viable, photolithographic techniques, imposes a limit on the resolution of a projected image. Conventional photo-lithographic techniques rely on light in the 436 to 365 nanometer (nm) wavelength regime. These are the wavelengths used respectively by commercially popular G-line and I-line steppers. Conventional G-line steppers produce masking-layer apertures of no smaller than approximately 0.6 microns (600 nanometers) in width or diameter. Conventional I-line steppers produce masking-layer apertures of no smaller than approximately 0.4 microns (400 nanometers) in width or diameter. The minimum aperture size of these aperture-defining technologies place like lower bounds on the width or diameter of each feature created in the underlying substrate.